Stabilized mineral oil lubricant compositions



United States Patent STABILIZED MINERAL OIL LUBRICANT COMPOSITIONS TroyL. Cantrell, Lansdowne, and Herschel G. Smith, Wallingford, Pa.,assignors to Gulf Oil Corporation, Pittsburgh, Pa., a corporation ofPennsylvania No Drawing. Application June 17, 1949, Serial N- 99,889

1 Claim. (Cl. 252-515) This invention relates to stabilized mineral oillubricant compositions, and more particularly, it relates to mineral oillubricants which have been stabilized against oxidative deterioration.More specifically, this invention is concerned with improvements inmineral lubricant compositions containing addition agents of the typedisclosed inv the copending application of Smith, Cantrell and Peters,Serial No. 66,585, filed December 21, 1948, now U. S. Patent No.2,511,747, and assigned to the same assignee as the present application.

Plain mineral lubricating oils often prove unsatisfactory in thelubrication of internal combustion engines of all types, particularlywhen severe operating conditions are encountered, because of theoxidative deterioration of the oil with the attendant deposition on theengine surfaces of varnish, gum or sludge. Furthermore, many lubricatingoil compositions which may be satisfactory for the lubrication of othermechanisms have been found wholly unsuitable for use as turbine oils.

The formation of varnishes, gums and sludges on engine surfaces isgenerally ascribed, at least in part, to oxidation effects on minerallubricating oils. The problem of oxidation is further aggravated inturbinue oils because in normal use turbine oils become rapidlycontaminated with water.

While the type of additive disclosed and claimed-in copendingapplication, Serial No. 66,585, confers a remarkably eifective oxidationstability on mineral lubricating oils, the oils in use sometimes acquirea dark color, albeit their oxidation stability remains generallyunimpaired. This darkening in color, although insignificant from thestandpoint of oxidation stability, is important from the standpoint ofthe consumer, because to him, the darkening in color during use of theoil would normally be indicative of degradation, whether or not that isthe fact. It would be advantageous, therefore, to provide minerallubricating oils which remain light in color even after extended periodsof use.

The principal object of this invention, then, is to provide mineral oillubricant compositions which, in addition to being stabilized againstoxida'tive deterioration, will not materially be darkened in colorduring use. Other objects willbe apparent from the following detaileddescription.

These objects are accomplished by the present invention which resides inthe provision of a mineral lubricating oil containing (1)2,6-ditertiarybutyl-4-methyl phenol and a non-resinous condensationproduct of N- dimethylaniline and formaldehyde, the mol ratio offormaldehyde to N-dimethylaniline ranging from 0.5 :1 to 10:1 and thecondensation of said product having been carried out in the presence ofan activatedclay catalyst at a temperature not in excess of 350 F. tocondense together the two reactants.

We have found that when a mineral lubricating oil is stabilized againstoxidative deterioration by the use of both of the additives set forthherein, darkening of the mineral lubricating oil in use is materiallyretarded. We have also found that the two additives unexpectedlysynergize each other; that is, the antioxidant life of a mineral oilcontaining both additives is greater than the sum of the antioxidanteffects obtained from the use of the individual additives alone.

As disclosed in U. S. Patent No. 2,265,582, 2,6-ditertiarybutyl-4-methylphenol is by itself a good antioxidant. As disclosed in copendingapplication Serial No. 66,585, the non-resinousN-dimethyaniline-formaldehyde condensation product prepared in thepresence of an activated clay is in itself an excellent antioxidant, itbeing generally more potent than 2,G-ditertiarybutyl-4-methyl phenol,particularly under service conditions involving high temperatures. Ourinvention resides in using both of these antioxidants in one minerallubricating oil to obtain as new and unexpected results thestabilization of the color of the oil during use and a synergisticeffect on the oxidation stability of the oil.

As disclosed in copending application Serial No. 66,585, thenon-resinous N-dimethylaniline-formaldehyde condensation product isprepared by heating the reactants in the presence of an activated claycatalyst at a temperature not in excess of 350 F. to condense togetherthe two reactants. If the temperature of 350 F. is exceeded to anysubstantial extent, the condensation product formed tends to be resinousand insoluble. The preferred temperature for the condensation rangesfrom to 300 F. The proportions of the reactants used to prepare thecondensation product vary over a relatively wide range. As a lower limitthe mol ratio of formaldehyde to N- dimethylaniline should not be lessthan 0.5 1. However, it is preferred to employ larger amounts offormaldehyde relative to the N-dimethylaniline since more potentantioxidants are obtained thereby. Accordingly, the mol ratio offormaldehyde to N-dimethylaniline may be as high as 10:1. Ordinarily itis preferred to use from 5 to 10 per cent by weight of an activated claycatalyst based on the total weight of the reactants. However, smalleramounts, as low as 1 per cent by weight, and larger amounts, as high as20 per cent by weight, can be used; but larger amounts than about 10 percent by weight are ordinarily not necessary. Contrary to what may beexpected from the nature of the reactants, highly condensed, insolubleresinous products are not obtained. On the contrary, when the abovereactants are condensed in ac cordance with the copending applicationabove referred to, there are obtained light-colored condensationproducts which are non-resinous and which are readily soluble in mineraloils.

In lieu of formaldehyde in the condensation reaction, anyformaldehyde-yielding compound can be used, such as paraformaldehyde,dioxymethylene and trioxymethylene. In such case, the amount offormaldehyde-yielding compound used is based on the equivalent number ofmols of formaldehyde yielded within the range of proportions offormaldehyde set forth hereinabove. Accordingly, as used in the appendedclaims, the term formaldehyde is intended to includeformaldehyde-yielding compounds as well as formaldehyde itself.

Various activated clays are employed in the preparation of theN-dimethylaniline-formaldehyde condensation products. Such materials arewell known in the art and comprise a natural clay, such as bentonite,fullers earth, floridin and smectite, which has been acid treated inorder to activate the clay. These materials are described in U. S.Patent No. 1,898,165, for example.

In preparing the N-dirnethylaniline-formaldehyde condensation product,the reactants and catalyst are placed in a reaction vessel which is thenclosed and the mixture is heated with agitation until all of theformaldehyde or formaldehyde-yielding compound has been consumed. Atthis time, the water which is formed as a result of the condensation isremoved, preferably under vacuum, and the dehydrated condensationproduct is then filtered to remove the activated clay catalyst. If it isdesired, the condensation product may be prepared in a concentrate in amineral lubricating oil which may then be diluted with additional oil tothe final concentration desired. These condensation products are liquidsor crystalline solids and contain in combination the reactants employedin their preparation. As shown in the copending application hereinabovereferred to, the use of an activated clay as a catalyst is essential inthe preparation of the condensation products; otherwise black,insoluble, resinous condensation products are obtained and theantioxidant potency of the product is adversely affected.

The other agent, 2,6-ditertiarybutyl-4-methyl phenol, which we employ inthe lubricant of this invention, may be obtained from any suitablesource. One method of preparing 2,6-ditertiarybutyl-4-methyl phenol isdisclosed in U. S. Patent No. 2,265,582 and comprises alkylating paracresol with isobutylene until no more isobutylene reacts with the paracresol.

For the purposes of the present invention, theN-dimethylaniline-formaldehyde condensation product and2,6-ditertiarybutyl-4-methyl phenol are added to mineral lubricatingoils in minor amounts, say in a total amount of both additives of from0.01 to 1.0 per cent by weight on the mineral oil, sufficient to inhibitoxidative deterioration of the oil. Larger amounts of our additives maybe used if desired, but it is ordinarily unnecessary to do so. Withinthe total amounts of both additives set forth herein, each additive mayrange from 20 to 80 per cent by weight of the total, i. e., in a weightratio of from 1:4 to 4:1. Stated in another way, in order to obtain thedesired results as to retardation of darkening in color, at least 20 percent by weight of the total additives should be2,6-ditertiarybutyl-4-methyl phenol; and in order to obtain thebeneficial effects of the condensation product in prolonging oxidationstability, at least 20 per cent by weight of the total additives shouldbe the N-dimethylaniline-formaldehyde condensation product. Thesynergistic effects of the additives on each other with respect toantioxidant potency are also limited by the foregoing, but are obtainedover the whole range of proportions of total additive disclosed herein.

The following examples are illustrative of our invention. The oxidationtest referred to is a standard test designated ASTM D 943-47 T. Briefly,the test comprises subjecting the oil sample to oxygen at a temperatureof 95 C. (203 F.) presence of water and an ironcopper catalyst, anddetermining the time required to build up a neutralization number of 2.The flow of oxygen is maintained at 3 liters per hour. The remarkablyeffective stability to oxidation of the mineral oil lubricantcompositions containing our new addition agents, the color improvementsand the synergistic effects are illustrated by the results shown in thefollowing examples:

Example I .A portion of turbine oil stock was treated with 0.2 per centby weight of (A) 2,6-ditertiarybutyl-4- methyl phenol, and anotherportion of this stock was treated with 0.2 per cent by weight of (B) thecondensation product of 1 mol of N-dimethylaniline and 2 mols offormaldehyde, prepared in the presence of 10 per cent by weight ofFiltrol (activated clay) as set forth in the above-identified copendingapplication. A third portion was treated with both 0.2 per cent byweight of (A) 2,6- ditertiarylbutyl-4-rnethyl phenol and 0.2 per cent byweight of (B) the condensation product of N-dimethylaniline andformaldehyde. The base oil, the oil blended with (A), the oil blendedwith (B), and the oil blended with both (A) and (B) exhibited thefollowing properties:

Bisle Base Base 1 on on @53 Base 0911' 0911' ing taintam- O11 0.2% mg mgof (A) 0.2% 0.2% and of (A) of (B) 02% of (B) Gravity, API 28. 5 28. 428. 4 28. 3 Viscosity, SUV, 100 F (110 (111 010 612 Flash, 00, F 490 190490 490 Four, F +5 +5 +5 +5 Color, NPA 2. 5 2. 5 2. 5 2. 5 OxidationTest, ASTM D943-47T:

Time Oxidized, Hrs 210 400 1, 200 2,000 Neutralization No 2.0 2.0 2. 2.0Expected Time Oxidized, Hrs... 1, 000 Increase Over Expected TimeOxidized, Hrs 400 Color of Oil After 14 Day dation Test, NPA 5.0 2. 4. 52.

Example II.-A portion of turbine oil stock was treated with 0.1 per centby weight of (A) 2,6-ditertiarybutyl-4-methyl phenol, and anotherportion of this stock was treated with 0.1 per cent by weight of (B) thecondensation product of 2 mols of N-dimethylaniline and 3 mols offormaldehyde prepared as described in the above identified copendingapplication. A third portion was treated with both 0.1 per cent byWeight of (A) 2,6- ditertiarybutyl-4-methyl phenol and 0.1 per cent; by

weight of (B) the condensation product of N-dimethylaniline andformaldehyde. The base oil, the oil blended with (A), the oil blendedwith (B), and the oil blended with both (A) and (B) showed the followingresults:

Brsle Base Base 1 on on $32: Base ing aintam- O11 0.1% mg mg of (A) 0.1%0.1% and of (A) of (B) of (B) C0101, NPA l. 5 l. 5 1 5 1. 5 OxidationTest, ASTM D9 Time Oxidized, Hrs. 195 280 650 1, 800 Neutralization No2.0 2.0 2.0 2.0 Expected Time Oxidized, Hrsm. 930 Increased OverExpected Time Oxidized, Hrs 870 Color of Oil After 14 Days OxidationTest, NPA 5. 0 2.0 4. 5 2.0

Example III.A portion of turbine oil stock was treated with 0.3 per centby weight of (A) 2,6-ditertiarybutyl-4-methyl phenol, and anotherportion of this stock was treated with 0.3 per cent by weight of (B) thecondensation product of 2 mols of N-dimethylaniline and 1 mol offormaldehyde prepared as described in the aboveidentified copendingapplication. A third portion was treated with both 0.3 per cent byweight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.3 per cent byweight of (B) the condensation product of N-dimethylaniline andformaldehyde. The base oil, the oil blended with (A), the oil blendedwith (B), and the oil blended with both (A) and (B) showed the followingresults:

Example IV.A portion of turbine oil stock was treated with 0.1 per centby weight of (A) 2,6-ditertiarybutylt-methyl phenol, and another portionof this stock was treated with 0.2 per cent by weight of (B) thecondensation product of 2 mols of N-dimethylaniline and 3 mols offormaldehyde prepared as described in the above-identified copendingapplication. A third portion was treated with both 0.1 per cent byweight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.2 per cent byweight of (B) the condensation product of N-dimethylaniline andformaldehyde. The base oil, the oil blended with (A), the oil blendedwith (B), and the oil blended with both (A) and (B) showed the followingresults:

Bgsle Base Base 1 on on Base 9 0911' ing amtam- Oil 0.1% mg mg of (A)0.1% 0.2% and of (A) of (B) 0.2%

Gravity, API 28.8 28. 7 28. 7 28.8 Viscosity, SU", F 303 301 302 303Oxidation Test, ASTM D943-47T:

Time Oxidized, Hrs 1, 530 Neutralization No 2.0 Expected Time Oxidized,H 1,165 Increase Over Expected Time Oxidized, Hrs 365 Color of 011 After14 Days Oxidation Test, NPA 8.0 2.0 8.0 2.0

The preceding examples clearly illustrate the remarkable properties ofour new mineral oil lubricant composi; tions. The color tests madeduring oxidation show that the base oil and the oil containing theN-dimethylanilineformaldehyde condensation products alone turned darkduring oxidation, while the oil containing both additives, in accordancewith the present invention, retained its pristine color. The color testreferred to is described in ASTM Standards on Petroleum Products andLubricants, November 1948, pages 105-109 (ASTM D 155- 45 T). A NationalPetroleum Association (NPA) color number of 2 designates an oil slightlydarker than cream white, namely extra pale. Also significant is the factthat while the lubricating oil containing theN-dimethylaniline-formaldehyde condensation products alone turned darkduring oxidation, only a relatively small amount of2,6-ditertiarybutyl-4-methyl phenol need be added to give an NPA colorof 2.

In addition to color improvement, the above examples clearly show theunexpected synergistic efiect with respect to antioxidant potencyobtained in accordance with the present invention. In preceding ExampleI, for instance, the lubricating oil containing the combination ofadditives was much more stable to oxidation than oils containing theadditives separately. The oil containing only2,6-ditertiarybutyl-4-methyl phenol had an antioxidant life of 400hours. The oil containing only the N-dimethylaniline-formaldehydecondensation product had an antioxidant life of 1200 hours. It would beexpected, therefore, that an oil containing both additives would have anantioxidant life of about 1600 hours. However, the test shows that theimproved oil of this invention had an antioxidant life of 2000 hours,indicating an unexpected synergistic effect.

The above examples also show the remarkable oxidation stability impartedto mineral oil lubricant compositions by the use of the addition agentsdescribed. Mineral oil lubricant compositions containing these additionabents are therefore eminently suited for use where the operatingconditions are extremely severe, as in Diesel,

tank and truck engines, and in the lubrication of steam turbines.Furthermore, the beneficial effects of our invention may be applied toall types of lubricating oil basekstocks, that is, parafiinic,naphthenic and mixed base stoc s.

If desired, other known addition agents may be incorporated intolubricant compositions prepared in accordance with our invention. Forexample, pour point depressants, extreme-pressure agents, and the likemay be added. Resort may be had to such modifications and variations asfall within the spirit of the invention and the scope of the appendedclaim.

We claim:

A lubricant composition comprising a major amount of a minerallubricating oil and minor amounts, in a total of from 0.01 to 1 per centby weight of said oil, of: (1) 2,6-ditertiarybutyl-4-methyl phenol; and(2) a nonresinous condensation product of 1 mol of N-dimethylaniline and2 mols of formaldehyde, the condensation of said product having beencarried out in the presence of an activated clay catalyst at atemperature not in excess of 350 F. to condense together the tworeactants; the amounts of (1) and (2) with respect to each other beingin a weight ratio ranging from 1:4 to 4:1.

References Cited in the file of this patent UNITED STATES PATENTS2,202,825 Brandes June 4, 1940 2,225,533 Dewey Dec. 17, 1940 2,375,168Hardman May 1, 1945 2,410,652 Grifiin Nov. 5, 1946 2,440,530 Yates Apr.27, 1948 2.511,747 Smith et al. June 13, 1950 OTHER REFERENCESKalichevsky, Lubricating Oil Additives, Petroleum Refiner, September1940, pages and 86.

Georgi, Motor Oils and Engine Lubrication, Rein hold Pub. Co., 1950,pages 27 and 28. i

